Growth Of Poly Research Articles

Preparation, characterization and electrocatalytic studies on hybrid films of electropolymerized manganese tetra(o-aminophenyl)porphyrin and adsorbed flavins

Abstract Hybrid films composed of electropolymerized manganese tetra( o -aminophenyl)porphyrin (MnTAPP) and flavin adenine dinucleotide (FAD), or flavin mononucleotide (FMN), or riboflavin (RF) adsorbed film modified electrodes have been prepared from aqueous acidic solutions. The hybrid films showed four redox couples. Electrochemical quartz crystal microbalance combined with cyclic voltammetry was used to study the in situ growth of poly(MnTAPP) film as well as poly(MnTAPP)/FAD hybrid film. The stability of the adsorbed flavins molecules increased in the presence of poly(MnTAPP) film. Hybrid films have shown surface confined electron transfer characteristics and the peak potentials of redox couples are pH dependent. The electrocatalytic behavior of poly(MnTAPP)/Flavin hybrid films toward reduction of oxygen, NAD + , nitrite and S 2 O 8 2 - was investigated. Oxygen reduced at lesser potential on hybrid film compared to unmodified electrode. The electrocatalytic activity of hybrid films showed the order poly(MnTAPP)/FAD > poly(MnTAPP)/FMN > poly(MnTAPP)/RF toward reduction of NAD + and NO 2 - .

Monitoring formation of poly(neutral red) film by EQCM

An electrochemical quartz crystal microbalance (EQCM) is employed for monitoring the growth of poly(neutral red) films on platinum in the electrolytic solution containing 5.0 mmol dm−3 neutral red, 0.3 mol dm−3 H2SO4, and 0.5 mol dm−3 Na2SO4. The in situ measurement of the frequency changes of the EQCM reveals that both the adsorption/desorption of neutral red and the formation of poly(neutral red) film can be observed together with anion sorption/desorption during the redox transformation of the polymer, and that the polymerization rate of neutral red increases slowly before the 11th cycle and then increases quickly with increasing number of potential cycles.

Growth of poly(methyl methacrylate) brushes on silicon surfaces by atom transfer radical polymerization

AbstractPoly(methyl methacrylate) (PMMA) brushes are grown by surface‐initiated atom transfer radical polymerization on silicon surfaces at various polymerization temperatures. Kinetic studies show that the layer thickness scales linearly with the degree of polymerization of the polymers under some conditions, indicating a constant graft density of the surface‐attached chains. At high temperatures, the layer growth is a controlled process only for short reaction times, and after a rapid increase, the film growth levels off, and a constant thickness is obtained. At lower reaction temperatures, polymers with a lower polydispersity are obtained, but at the expense of a much slower growth rate. Accordingly, intermediate temperatures yield the highest film thickness on experimentally feasible timescales. The reinitiation of these surface‐grafted PMMA chains at room temperature to either extend the chains or grow a chemically different polyglycidylmethacrylate block demonstrates the presence of active ends and the living nature of the surface‐grafted PMMA chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1758–1769, 2006

Atomic Force Microscopic Observation of in Vitro Polymerized Poly[(R)-3-hydroxybutyrate]: Insight into Possible Mechanism of Granule Formation

Atomic force microscopy (AFM) was used to study the formation and growth of poly[(R)-3-hydroxybutyrate] (PHB) structures formed in the enzymatic polymerization of (R)-3-hydroxybutyryl coenzyme A [(R)-3-HBCoA] in vitro. Poly(3-hydroxyalkanoate) (PHA) synthase (PhaC(Re)) from Ralstonia eutropha, a class I synthase, was purified by one-step purification and then used for in vitro reactions. Before the reaction, PhaC(Re) molecules were deposited on highly oriented pyrolytic graphite (HOPG) and observed as spherical particles with an average height of 2.7 +/- 0.6 nm and apparent width of 24 +/- 3 nm. AFM analysis during the initial stage of the reaction, that is, after a small amount of (R)-3-HBCoA had been consumed, showed that the enzyme molecules polymerize (R)-3-HBCoA and form flexible 3HB polymer chains that extend from the enzyme particles, resulting in the formation of an enzyme-nascent PHB conjugate. When a sufficient amount of (R)-3-HBCoA was used as substrate, the reaction rapidly increased after the first minute followed by a slow increase in rate, and substrate was completely consumed after 4 min. After 4 min, spherical granules continued to grow in size to form clusters over 10 um in width, and in later stages of cluster formation, the cluster developed small projections with a size of approximately 100-250 nm, suggesting qualitative changes of the PHB clusters. Moreover, the high-resolution AFM images suggested that globular structures of approximately 20-30 nm apparent width, which corresponds to the size of PhaC(Re), were located on the surface of the small PHB granule particles.

Observation of the concentric diffractive banding on the spherulites of poly(ethylene oxide) by a dynamic method

The growth of poly(ethylene oxide) (PEO) spherulites was observed synchronously with a polarized optical microscope, which was equipped with a video detector, and so the whole growing process of the PEO spherulites was dynamically recorded as a movie. There was a series of concentric diffractive bands on the surface of the PEO spherulites; furthermore, the diffractive banding did not exist until at least two independent PEO spherulites came into contact with each other. However, the formation of the diffractive banding on the PEO spherulites was also related to the crystallization conditions. It was concluded qualitatively that the diffractive banding formed more easily at the crystallization temperature with a high degree of supercooling, and this was explained in kinetic terms. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2454–2458, 2005

Spherulitic morphology and growth of poly(vinylidene fluoride)/poly(3-hydroxybutyrate-co-hydroxyvalerate) blends by optical microscopy

Spherulitic morphology and growth of poly(vinylidene fluoride)/poly(3-hydroxybutyrate-co-hydroxyvalerate) blends by optical microscopy

Spherulitic morphology and growth of poly(vinylidene fluoride)/poly(3-hydroxybutyrate- co-hydroxyvalerate) blends by optical microscopy

Poly(vinylidene fluoride) (PVDF) and poly(3-hydroxybutyrate- co-hydroxyvalerate) (PHBV), both semicrystalline polymers, are miscible as shown by the single glass transition temperature over the entire composition range. Morphology of PVDF/PHBV blends was investigated by optical microscopy under two different crystallization conditions. PVDF showed the spherulitic morphology at 150 °C in the PVDF/PHBV blends, where PHBV acted as the noncrystallizing component. PHBV also showed the spherulitic morphology within the matrix of the pre-existing PVDF crystals when PVDF/PHBV blends were quenched from the melt to the crystallization temperature below the melting point of PHBV. The spherulitic growth of PHBV was investigated as the function of both blend composition and crystallization temperature.

Effect of impact modification on slow crack growth in poly(vinyl chloride)

The effect of impact modification on slow crack growth in a poly(vinyl chloride) (PVC) compound was examined in order to test a methodology for predicting long-term creep fracture from short-term tension-tension fatigue tests. In all cases the crack propagated in a stepwise manner through a crack tip craze zone. Step length was analyzed in terms of the Dugdale model for a crack tip plastic zone. The overall crack growth rate in fatigue and creep followed the conventional Paris power law with the same power 2.7, da/dt = Af ΔKI2.7 and da/dt = BKI2.7,respectively. The effects of frequency, temperature, and R-ratio (the ratio of the minimum to maximum stress intensity factor in the fatigue loading cycle) on the Paris prefactor were determined. Crack growth rate was modeled as the product of a creep contribution that depended only on the maximum stress intensity factor and a fatigue contribution that depended on strain rate da/dt = BfKI,max2.7 (1 + C e, where C is a coefficient defining the strain rate sensitivity. A linear correlation allowed for extrapolation of the creep prefactor Bf from fatigue data. Impact modification decreased Bf but had no effect on C.

Stepwise fatigue crack propagation in poly(vinyl chloride)

AbstractThe kinetics and mechanism of fatigue crack growth in poly(vinyl chloride) (PVC) compounds of different molecular weight were studied. The fatigue crack propagation rate of all the PVC compounds followed the Paris law: da/dt = Af ΔK. Fatigue crack propagation rate, as reflected by the pre‐factor Af in the Paris law, was highly dependent on molecular weight of the resin, strain rate, and temperature. A stepwise mechanism of fatigue crack propagation was observed in all the PVC compounds. Steps were formed by discontinuous growth of the crack through a single craze in the shape of a narrow strip. Step length and lifetime were used to characterize fatigue crack propagation. J. Vinyl Addit. Technol. 10:5–10, 2004. © 2004 Society of Plastics Engineers.

Growth of poly(pseudorotaxane) on gold using host-stabilized charge-transfer interaction.

A novel supramolecular polymer (poly(pseudorotaxane)) in which the repeating units are linked by host-stabilized charge-transfer interaction between the guest molecules is grown on gold and characterized.

Growth and electrochemical activity of the poly- l-lysine|poly- l-glutamic acid thin layer films: an EQCM and electrochemical study

Quartz crystal microbalance (QCM) measurement and cyclic voltammetry were used to study the layer-by-layer growth of poly- l-lysine (p-Lys) and poly- l-glutamic acid (p-Glu) thin films and their ability to act as support for redox relays between metal electrodes and redox species in organic electrolytes. The mass of the film grown from buffered solution at constant pH depends on the composition of the buffer used. The growth proceeds in several stages with different mass increments for each poly- l-lysine and poly- l-glutamic acid layer. Ferro/ferricyanide confined into the polypeptide films can play the role of a redox relay between the electrode surface and the organic electrolyte. This was demonstrated on the impregnated polypeptide film|1,2-dichloroethane interface with decamethylferrocene dissolved as redox species in the organic phase. The transport of the ferro/ferricyanide in the polypeptide film is the rate limiting step of the electron transfer process. The diffusion coefficient of the ferro/ferricyanide determined from voltammetric experiments was of the order of 10 −11–10 −12 cm 2 s −1. The bimolecular rate constant of the electron transfer reaction was found to be 0.2 cm s −1 M −1.

Crystal Growth in Poly(L‐lactide) Thin Film Revealed by in situ Atomic Force Microscopy

AbstractDirect visualization of crystal growth in poly(L‐lactide) thin films was carried out by using a temperature‐controlled atomic force microscopy (AFM). At the initial stage of crystallization, edge‐on lamellar crystals have nucleated and elongated. Subsequently, the edge‐on lamellar crystals showed S‐shaped morphology and changed their orientation from edge‐on manner to flat‐on one. The curvature of edge‐on lamellar crystal has been discussed in terms of inclination and distortion of polymer chains in the crystal. In addition, mechanism on the formation of flat‐on crystal from edge‐on lamellae was proposed as derivative growth on the basis of in situ AFM observation of crystal growth and enzymatic degradation. magnified image

Electrochemical growth of poly(3-dodecylthiophene) into porous silicon: a nanocomposite with tubes or wires?

A derivative of polythiophiene: poly(3-dodecylthiophene) (PT 12) has been used to fill electrochemically a porous silicon matrix. The composite, obtained by this way, should have a high third order nonlinear optical coefficient and good mechanical properties. SEM and TEM micrographs were taken after matrix dissolution in NaOH. Columns of polymer with the matrix pore shape show up like fingers. In consideration of the homogeneous filling profile of PT 12 measured by EDX and XPS and the low amount of polymer, we are probably dealing with tubes instead of wires.

Heterogeneous nucleation and growth of crystalline micro-bubbles around gas cavities formed in solution

Perfect single three dimensional crystals with the shape of bubbles can nucleate and grow encompassing gas filled cavities previously formed on solid substrates in aqueous solutions. Bubbles are double walled, both internal and external faces belonging to the cleavage calcite rhombohedron which separate the growth solution from the enclosed gas cavity. The bubbles thickness amounting to a few nanometers, while the size of the bubble is strictly related to that of the cavity ( of the order of a few micrometers), the surface-to-volume ratio is the highest obtained till now for 3D single crystals. A tentative model of nucleation and growth mechanisms of these peculiar objects is proposed. Growth morphology modifications due to the effect of impurities ( Li + and acetate ions) or to foreign gas bubbling in the growth solution (methane) are also described. A peculiar attention is paid to both mechanical and thermodynamic conditions to be fulfilled in order to nucleate crystals around gas cavities from solution and melt. By analysing growth and patterning of Cacarbonate hollow shells in reverse microemulsions along with the growth from melt of sodium disilicate around gas microcavities, we found the criterion ruling the nucleation and growth of poly- or single crystals around a gas cavity and outlined the major role played by the nature of the substrate. Finally, is proposed a new interpretation of hollow shaped crystals, recently found in methane-derived carbonate rocks (Western Alps-Italy) and in late Cenozoic dolomites of the Bahamas.

Correlation of fatigue and creep crack growth in poly(vinyl chloride)

Slow crack growth in PVC pipe was studied in order to develop a methodology for predicting long-term creep fracture from short-term tension-tension fatigue tests. In all cases, the crack propagated continuously through a crack-tip craze. In fatigue, the density of drawn craze fibrils gradually increased with decreased frequency and increased temperature. At the lowest frequency, 0.01 Hz, the fibril density in fatigue approached that in creep. The kinetics of fatigue and creep crack growth followed the conventional Paris law formulations with the same exponent 2.7, da/dt = AfΔKI2.7, da/dt = BKI2.7, respectively. The effects of frequency, temperature and R-ratio (the ratio of minimum to maximum stress intensity factor in the fatigue loading cycle) on the Paris law prefactors were characterized. Comparison of frequency and R-ratio tests revealed that the fatigue contribution depended on strain rate. Therefore, at each temperature, crack growth rate was modeled as the product of a creep contribution that depended only on the maximum stress intensity factor and a fatigue contribution that depended on strain rate: (da/dt) = BKI,max2.7 (1 + Ce), where B is the prefactor in the Paris law for creep and C is a coefficient defining the strain rate sensitivity. A linear correlation allowed extrapolation of the creep prefactor (B) from fatigue data. The extrapolated values were systematically higher than the values measured directly from creep and only converged at Tg. The difference was attributed to damage of the craze fibrils during crack closure upon unloading in the fatigue cycle.

Scale‐up synthesis of hyperbranched poly(amidoamine)‐grafted ultrafine silica using dendrimer synthesis methodology in solvent‐free dry‐system

AbstractScale‐up synthesis of hyperbranched poly(amidoamine)‐grafted ultrafine silica was successfully achieved by using dendrimer synthesis methodology in solvent‐free dry‐system. The poly(amidoamine) was allowed to grow from silica surface by repeating two steps: (1) Michael addition of methyl acrylate (MA) to amino group on the surface and (2) amidation of terminal ester group with ethylenediamine (EDA). MA was sprayed onto silica having amino group and the silica agitated at 300 rpm at 50 °C. After the reaction, unreacted MA was removed under vacuum. Then EDA was sprayed and the reaction was conducted at 50 °C with agitation. After the reaction, unreacted EDA was also removed under vacuum at 50 °C and MA was sprayed again. The percentage of poly(amidoamine) grafting onto the surface was determined to be 141% with repeated reaction cycles of eight‐times. However, the value was considerably smaller than that of the theoretical value. This indicates that the propagation of poly(amidoamine) dendron from silica surface was not achieved theoretically and hyperbranched poly(amidoamine) was grafted onto the surface because of steric hindrance of grafted polymer. In addition, the effect of initial amino group content on the growth of poly(amidoamine) from the surface was investigated. It was concluded that the method is suitable for the scale‐up synthesis of hyperbranched poly(amidoamine)‐grafted silica. Copyright © 2002 John Wiley & Sons, Ltd.

THE INFLUENCE OF MOLECULAR WEIGHT ON THE REGIME CRYSTALLIZATION OF POLY(TRIMETHYLENE TEREPHTHALATE)

An optical microscope equipped with a video photography system was used to monitor the spherulite growth of poly(trimethylene terephthalate) (PTT). The thermal stability of PTT in nitrogen atmosphere was assessed from the variations of the growth rates of spherulites at 180 and 190°C after the samples were equilibrated for 5 or 6 min at melting temperatures in the range of 270–305°C. The growth rates remained nearly constant for melting temperatures up to 290°C and then increased with increase in melting temperature. It is suspected that degradation and transesterification occur in PTT at high temperatures in the melt. Results in this study suggest that when the melt of PTT has been equilibrated at 290°C for 5 min in nitrogen, the subsequent crystallization behavior is nearly independent of the prior thermal history. Linear growth rates of crystallization were then measured in the temperature range of 165–218°C for the PTT samples with three different molecular weights. Kinetic analysis indicated that PTT exhibits a regime transition which appears to be dependent on the molecular weight, decreasing with increase in molecular weight. The effect of equilibrium melting temperature on the product of lateral and fold surface free energies, σσ e, and the transition temperature will be discussed.

REGIME CRYSTALLIZATION AND BANDED SPHERULITE OF POLY(TRIMETHYLENE TEREPHTHALATE)

An optical microscope equipped with a video photography system was used to monitor the spherulite growth of poly(trimethylene terephthalate) (PTT). Linear growth rates of crystallization were measured in the temperature range of 165–215°C for melt-pressed film. Kinetic analysis indicated that PTT exhibits a regime transition at and is clearly present irrespective of the drastic changes in the values of T m o, U * and T ∞. This transition is expected to shift to a higher temperature for solvent-cast films. The PTT thin films with thickness in the range of micrometers for polarized light microscopy (PLM) and of 10 nm for transmission electron microscopy were prepared by solvent casting. Both reflected and transmitted modes of PLM were used to obtain optical images. A clear change in morphology was detected for solvent-cast films after melt crystallization. Regular spherulites were exhibited for films crystallized at temperature (T c) between 180 and 200°C. Banded spherulites were observed between and 225°C. The results indicated that the distance between these concentric rings decreased with the reduction in sample thickness and crystallization temperature.

Detection of Intermediate During the Electrochemical Polymerization of Azure B and Growth of Poly(azure B) Film

The electrochemical polymerization of azure B has been studied using the rotating ring-disk electrode (RRDE) and the electrochemical quartz crystal microbalance (EQCM). The electrolytic solution consisted of 2.5 mmol dm−3azure B, 0.2 mol dm−3NaH2PO4 and 0.5 mol dm−3 NaCl with various pH values. An intermediate was generated at the disk electrode and was collected. The collection efficiency increases with decreasing ring potential as well as increasing rotation rate. Thus, the intermediate carries a positive charge and is not too stable. Based on the determination of the frequency response of the EQCM, the polymerization rate of azure B increases slowly before the fifteenth cycle, and then increases quickly with increasing number of potential cycles. The EQCM is a very useful tool for determination of the starting polymerization potential of azure B, which is 0.60 V (vs. SCE) in this case. The maximum frequency difference during the oxidation and reduction processes of poly(azure B) film in the solution with pH 3.0 is 174.7 Hz, which corresponds to a mass change of 0.99 µg cm−2.

Growth of Poly(methylene blue) Film and Properties of the Film

Growth of Poly(methylene blue) Film and Properties of the Film